The objectives of the proposed research are: (1) To design, construct and test a system for simultaneously irradiating cell cultures with microwaves and X-radiation at pre-selected and controlled elevated temperatures. (2) Using this system, to subject cells to a graded range of microwave power levels at controlled elevated temperatures; the microwave power levels will range from a few milliwatts/sq.cm to several watts/sq.cm. (3) Using cell survival and cell membrane damage as primary criteria, to determine whether or not the effects of microwave hyperthermia are different from water bath heating. (4) Using cell survival and cell membrane damage as primary criteria, to determine whether or not there are significant differences between the effects of: (a) Simultaneous X-irradiation and water bath heating, and; (b) Simultaneous X-irradiation and microwave-induced hyperthermia.